[linrad] RE: Linrad for microwaves

[leif@xxxxxxxxxx]

> I of course calibrated the Linrad system again after installing the  
> upverter, using a pulser etc as outlined on Leif's webpages, and feeding  
> the pulser etc into the input of my Upverter.
A re-calibration is not necessary when you change the wideband hardware,
it is normally adequate to do the calibration at the input of the RX2500
unit. Calibration at the WSE10700 input could perhaps be better in case
the pulser is not well matched to 50 ohms since impedance errors at the
2500 input could have a small influence on the 2.5 MHz filter characteristics. 

Another thing is (of course) that changing from two channels to a single 
channel requires a new calibration.

> PS  I found that most of my system birdies are 'fixed' and don't 
> move when  
> I change band segments with Linrad.  I could therefore cycle up 
> or down 25  
> KHz in Linrad to see which signals to ignore.
There should not be any fixed frequency spurs with the WSE converters.
That is an indication of interference that leaks into the system on
2.5 MHz or perhaps at audio frequencies.

> I still haven't installed the STAR ground at the new QTH.  I know 
> I should  
> do that but just haven't had time yet.  Even so, my center discontinuity  
> is not a significant problem.
This may be the reason that something leaks into the system. Try to
disconnect the 2.5 MHz inputs to see whether the leakage is at the 
input or output of the 2.5 MHz unit.

A quick fix could be to use both channels all the way from 144 MHz
where you can simply use a t-connector to feed both channels.
The spurs that leak into the system will most probably have the same
phase and amplitude relation so they should appear to have the same 
polarisation. Set the polarisation control to fixed polarisation
and turn the polarisation angle and ellipticity for the spurs to
go away. You can then change the cable lengths and possibly the 
amplitude ratios at the 144 MHz input for the microwave signals
to appear in the opposite polarisation. This way you will immediately
see (in the high resolution graph) whether a signal is a spur (red) 
or if it is a microwave signal (green).

Another thing you could do is to arrange two upverters so you can send
the signals from two microwave bands into linrad. You would loose 3 dB
S/N on the waterfall graph, but when you click on a signal, Linrad will
automatically select the correct band and you can see on the polarisation 
indicator which band it originates from. You would of course have to set 
the gain for the noise floors to be similar. The upverters would have
to shift the interesting parts of the microwave bands to the same 95 kHz 
segment on 144 MHz (of course). Having two complete systems you could 
monitor 4 microwave bands simultaneously. On bands with low activity
this might be a significant advantage. The 3 dB loss would probably not
be a problem since you should still be able to detect all the signals that
are strong enough for a regular qso. 

73

Leif / SM5BSZ


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